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Assortment of Issues with EFI on Mac

From: Jake Thomas
Subject: Assortment of Issues with EFI on Mac
Date: Fri, 30 Dec 2011 05:12:01 -0800 (PST)

//Using version 1.99 of Grub
Hello everyone, I've been meaning to submit these bugs for quite a while now, at least since summer, but have been busy with school and hadn't taken the time to figure the Grub mailing list out, and was at a loss as to how to go about submitting bugs.

I have been playing with Grub2 on a thumb drive. I didn't know why it wasn't booting on the Mac, and, after some research, found out about EFI v.s. BIOS. After some more research and head-banging, I made some working grub efi images, put them on my thumb drive, and I could boot Linux off my thumb drive on a Mac, which uses EFI, not BIOS.

I encountered some issues.

One I call the "temptation error". If Linux is on the internal hard drive of my Macbook, and I get booted into Grub off my thumb drive via EFI, and I tell it to load Linux off the thumb drive, Grub finds the Linux on the internal hard drive too tempting and usually boots that instead. The kernel and initrd were the same name and path on both the internal hard drive and thumb drive, so it's not like it got possessed and started looking around for Linuxes to boot.

When you are on a Macbook with Linux on the internal hard drive with a kernel and initrd of the same name and path as the kernel and initrd on a thumb drive with a bootable grub EFI image, and you boot into EFI Grub off the thumb drive, it seems to, on average, actually succeed in booting off the thumb drive rather than the internal about 1 in every 14 times. It's more like it randomly picks a number between 12 and 17 or so, and that's how many more attempts it will take to get to the next successful attempt to boot off the thumb drive rather than the internal.

Another one is an often patternistic blackout bug. I can boot my MacBook off my thumb drive into EFI Grub, select to boot Linux off my thumb drive, and boot Linux no problem (unless Linux exists on the internal). Then the next time I try, it might black the screen out. In fact, pressing enter or escape or any key doesn't do anything, so it actually is crashed-out, rather than the screen simply having gone black.
But here's the interesting part: If I save a copy of grub.cfg to my desktop (the one in the EFI grub prefix) and then delete it off my thumb drive, and then boot my MacBook off my thumb drive, I successfully get to a command line and can boot Linux "by hand." Then I can put the grub.cfg back on, and it will work next time. Sometimes it follows a simple AB pattern of blacking out, me deleting grub.cfg, getting to a command line, me putting grub.cfg back on, Grub booting correctly with a menu and background image and all, and then the cycle repeats. Though recently I haven't experienced a strict cycle; it's more of a certain probability of blacking out, to which the fix is to delete grub.cfg, boot without it, then put it back on.

And here's a couple of minor bugs (but they still ought to be fixed):

Grub doesn't load a grub.cfg file if it has extra carriage returns at the end. To someone who doesn't know this and is making a grub.cfg file by hand for, say, a thumb drive, this can cause a lot of frustration; it sure caused me a lot of frustration! Grub only loads a grub.cfg file if the last character is a part of the Grub script, usually a "}".

When I boot my thumb drive via EFI on my MacBook, it erroneously, for a brief moment, says "error: prefix not set" and then continues loading Grub to a menu with a background and everything (unless it blacks out). The prefix is indeed set and can be confirmed by command line.

Also, I have experienced issues with iMacs, but don't have enough definite testing to really report anything. It wasn't loading the background, had funny characters around the menu like it does when the font file isn't present, and it was in portrait rather than in landscape, and if I remember right, didn't even boot Linux.

I'm a big fan of Grub. I felt like I found heaven on Earth when I started understanding it and using it, because I was using syslinux before that (for thumb drives). Boy! Support for either EFI or BIOS, the ability to have a pretty background image, font of your choice, so many modules for anything...it's got so many great things to it! And if these kinks could be worked out, it'd be even better. If we really do switch to EFI, they better get fixed.


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